Blog: Posts from March, 2009

Northwind database has a cross-reference table EmployeeTerritories that link together an employee and a territory. Here is a user interface generated for this table by Data Aquarium premium project.

List of employee territories is filtered by a region.

Employee territory is displayed in edit form.

While completely function this type of user interface will still benefit if we display a collection of all territories right on the employee screen and allow user to check mark territories that is user is responsible for.

Creating a Placeholder Field For a List of Territories

Open ~/Controllers/Employees.xml data controller and modify the text of command1 as shown below. Notice the new field Territories just before the from clause. This field is used just as placeholder and an actual value is going to be provided by a business rule.

        <command id="command1" type="Text">
            <text>
                <![CDATA[
select
    "Employees"."EmployeeID" "EmployeeID"
    ,"Employees"."LastName" "LastName"
    ,"Employees"."FirstName" "FirstName"
    ,"Employees"."Title" "Title"
    ,"Employees"."TitleOfCourtesy" "TitleOfCourtesy"
    ,"Employees"."BirthDate" "BirthDate"
    ,"Employees"."HireDate" "HireDate"
    ,"Employees"."Address" "Address"
    ,"Employees"."City" "City"
    ,"Employees"."Region" "Region"
    ,"Employees"."PostalCode" "PostalCode"
    ,"Employees"."Country" "Country"
    ,"Employees"."HomePhone" "HomePhone"
    ,"Employees"."Extension" "Extension"
    ,"Employees"."Photo" "Photo"
    ,"Employees"."Notes" "Notes"
    ,"Employees"."ReportsTo" "ReportsTo"
    ,"ReportsTo"."LastName" "ReportsToLastName"
    ,"Employees"."PhotoPath" "PhotoPath",
    ,null "Territories"
from "dbo"."Employees" "Employees"
    left join "dbo"."Employees" "ReportsTo" on "Employees"."ReportsTo" = "ReportsTo"."EmployeeID"
]]>
            </text>
        </command>

Add new field to the list of fields.

<field name="Territories" type="String">
    <items style="CheckBoxList" dataController="Territories" 
        dataTextField="TerritoryDescription"/>
</field>

Modify editForm1 to include a reference to the field in the user interface of the form right after the FirstName field. We have specified 3 as number of columns for the field, which is supposed to be displayed as a check box list.

<dataField fieldName="LastName" columns="20" />
<dataField fieldName="FirstName" columns="10" />
<dataField fieldName="Territories" columns="3"/>

Run the sample application and start editing any employee record in form mode. Here is what you will likely see.

None of the check boxes is checked. We will add a business rule to populate the check boxes.

Creating a Business Rule to Populate an Existing Row

Open business rules class ~/App_Code/Class1.cs(.vb) that was created as described in the RowBuilder attribute introduction. Add the following method to the class.

C#:

[RowBuilder("Employees", "editForm1", RowKind.Existing)]
protected void PrepareExistingEmployeeRow()
{
    int employeeId = Convert.ToInt32(SelectFieldValue("EmployeeID"));
    List<EmployeeTerritories> territories = 
        EmployeeTerritories.Select(employeeId, null, null, null, null);
    StringBuilder sb = new StringBuilder();
    foreach (EmployeeTerritories et in territories)
    {
        if (sb.Length > 0)
            sb.Append(",");
        sb.Append(et.TerritoryID);
    }
    UpdateFieldValue("Territories", sb.ToString());
}

VB:

Protected Sub PrepareExistingEmployeeRow()
    Dim employeeId As Integer = Convert.ToInt32(SelectFieldValue("EmployeeID"))
    Dim territories As List(Of EmployeeTerritories) = _
        EmployeeTerritories.Select(employeeId, Nothing, Nothing, Nothing, Nothing)
    Dim sb As StringBuilder = New StringBuilder()
    For Each et As EmployeeTerritories In territories
        If sb.Length > 0 Then
            sb.Append(",")
        End If
        sb.Append(et.TerritoryID)
    Next
    UpdateFieldValue("Territories", sb.ToString())
End Sub

The name of the business rule method is irrelevant. The rule will be automatically invoked when data controller Employees is preparing data for editForm1 view and the form will be displaying an existing row. This method is called for each row returned to the client. Data Aquarium Framework only returns the exact number of rows that are requested by a client view.

Method SelectFieldValue is inherited from the base class BusinessRules and allows to access values that will be returned for a row that is being built at this moment. We are obtaining a list of employee territories via business object EmployeeTerritories.

Next we are creating a comma-separated list of territory IDs and update the value of the Territories field with the result accumulated in an instance of System.Text.StringBuilder. Please make sure to add System.Text namespace in the list of imported namespaces.

Lookup item style CheckBoxList is designed to automatically handle comma separated lists of values.

Here is how editForm1 looks when we select a row. Text corresponding to each territory of selected employee is automatically matched to an ID of each employee territory.

Here is how eidtForm1 is transformed when user clicks on Edit button.

Conclusion

RowBuilder attribute allows providing calculated field values for new and existing rows returned to a client script running in a browser. You can create fields that don't actually exist in your database and figure their values on-the-fly.

There is still work to do when you need to save values of calculated fields. We will review this in the next post dedicated to ControllerAction attribute.

Latest update of Data Aquarium Framework introduces a new and much improved method of extending framework with custom business logic. You can take full advantage of declarative user interface of data controllers custom form templates, while having a significant control over data processing.

About Business Rules

ASP.NET development model makes it very easy for developers to mix user interface code and business logic code. It is just too tempting to write a few lines of a business rule that will be executed in response to a user interface control event. This leads to expensive maintenance.

We have put a significant effort into preventing such code blending from happening in applications built with Data Aquarium Framework. The first step was to introduce custom action handlers and data filters.

The new release builds on top of these two features and uses attribute-based approach to business rule development.

We will start review of business rules with RowBuilder attribute.

Sample Web application

Generate a sample Data Aquarium application from Northwind database.  Leave MyCompany as a default namespace. Make sure to request generation of business logic layer. We will use generated business objects to enhance our business rules whenever we need to access data. Note that if you generate your application with Membership support enabled then you will have to sign into your application in order to see any data presentation.

Open generated project in Visual Studio 2008 or Visual Web Developer 2008 and add a new class Class1 to ~/App_Code folder of your application. Our new class will inherit its base functionality from  BusinessRules class of MyCompany.Data namespace.

C#:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using MyCompany.Data;

public class Class1: BusinessRules
{
    public Class1()
    {
    }
}

VB:

Imports Microsoft.VisualBasic
Imports MyCompany.Data

Public Class Class1
    Inherits BusinessRules

End Class

Open file ~/Controllers/Employees.xml and add attribute handler to dataController element.

<dataController name="Employees" conflictDetection="overwriteChanges" 
    label="Employees" xmlns="urn:schemas-codeontime-com:data-aquarium"
    handler="Class1">

This will hook your business rules to Employees data controller. Your business rules will be universally applied whenever a reference to a data controller is made. You business rules will be invoked when your application is utilizing DataViewExtender or ControllerDataSource, when you export data or create new employees in data lookups.

The same set of business rules can be applied to multiple data controllers.

Building New Rows

The first rule will be assigning employee ID of company's CEO to ReportsTo field of any new employee record.

Add the following method to Class1.

C#:

[RowBuilder("Employees", "createForm1", RowKind.New)]
protected void PrepareNewEmployeeRow()
{
    using (SqlText findCEO = new SqlText(
        "select EmployeeID, LastName from Employees where ReportsTo is null"))
    {
        if (findCEO.Read())
        {
            UpdateFieldValue("ReportsTo", findCEO["EmployeeID"]);
            UpdateFieldValue("ReportsToLastName", findCEO["LastName"]);
        }
    }
}

VB:

<RowBuilder("Employees", "createForm1", RowKind.New)> _
Protected Sub PrepareNewEmployeeRow()
    Using findCEO As SqlText = New SqlText( _
        "select EmployeeID, LastName from Employees where ReportsTo is null")
        If findCEO.Read() Then
            UpdateFieldValue("ReportsTo", findCEO("EmployeeID"))
            UpdateFieldValue("ReportsToLastName", findCEO("LastName"))
        End If
    End Using
End Sub

The protection level of this method is only important if you are planning to create hierarchies of business rule classes.

The name of the method plays no role at all. Name your business rules methods to reflect their purpose.

The method is automatically called whenever a new row is about to be returned to user interface components by Employees data controller. Typically this will happen when end user is creating a new record. There is also a restriction on the presentation view that will ensure method execution when createForm1 is presenting data. You can apply multiple RowBuilder attributes to the same method if the same business logic is executed by other controllers and/or views.

Use method UpdateFieldValue to assign any default values to fields of a new row.

Class SqlText is a utility provided with Data Aquarium Framework to give you a simple and efficient way of querying a database.

Run the sample application and start creating a new employee record. Scroll to the bottom of the screen to see the result of our effort.

Next post will show how to manipulate fields of existing rows and demonstrate new look item style CheckBoxList.

The new lookup item style is featured in Membership user manager. Select any user and start editing a record. A menu of check boxes is presented to help you select user roles.